A popular non-volatile solid state memory in use today is flash memory (both NAND and NOR types). Flash memory is characterized by not being “write-symmetric” when writing data. To illustrate, each cell of a flash memory can be written from a value of “1” to a value of “0” independently of other cells. However, to change a cell back to a value of “1” a relatively large group of cells (called an “erase block”) are set to a “1” value as a group. An erase group might contain hundreds of kilobytes or even several megabytes, and flash management systems that manage frequent updates of small chunks of data may implement relatively complex logic to preserve valid data that may be stored at other locations in the erase block.
In recent years several new “write-symmetric” non-volatile memory technologies have been introduced that do not have the non-symmetry as described for flash memory, such as Resistive RAM (also known as RRAM or ReRAM), and Magnetic RAM (also known as MRAM), as illustrative examples. In these technologies, a cell may be written in both directions—from “1” to “0” and from “0” to “1” without imposing a similar operation on cells that neighbor the cell being written. As a result, it is possible to directly over-write a page of ReRAM or MRAM memories with new data regardless of the previous contents of the written page, something that is not possible with flash memories. Resistance-based non-volatile memories and other new “write-symmetric” non-volatile memories may significantly differ from other non-volatile memories, such as flash memories, in other structural and operational respects.